Most human cancer cells are resistant to apoptosis. Among the major regulators of apoptosis are the Bcl-2 family of proteins. An emerging cancer therapeutic strategy is directly activating the apoptotic pathways by inhibiting the activity of ani-apoptotic Bcl-2 proteins or promoting the function of pro-apoptotic Bcl-2 proteins. However, many of these strategies target the interaction among various Bcl-2 proteins, particularly the interaction between pro- apoptotic and anti-apoptotic Bcl-2 proteins. Due to functional redundancy among Bcl-2 proteins, these approaches are likely effective only on limited tumor types or display non-specific killing activities. As an important pro-apoptotic Bcl-2 protein, Bax s involved in the development of tumors, and Bax activation has been linked to apoptosis in lung tumors. Given that Bax alone is sufficient to initiate apoptosis in almost all apoptotic paradigms, direct activation of Bax by small molecule compounds could induce death of Bax-expressing tumor cells. Our preliminary studies using in silico screening of large chemical libraries identifid a small molecule predicted to bind to the Bax hydrophobic groove. This compound is able to activate Bax, leading to Bax-dependent tumor cell apoptosis and inhibition of mouse tumor growth. The following specific aims are proposed: 1) Examine the mechanisms by which the Bax activator inhibits tumor growth in mice. We will test the ability of the Bax activator to inhibt the growth of transplanted human tumors in mice as well as spontaneous mouse lung tumors. Furthermore, we will investigate whether the active compound acts synergistically with other therapeutic drugs to inhibit the growth of tumors. 2) Improve the ability of Bax activators to activate Bax, induce apoptosis and inhibit tumor growth. Ligand-based analyses will be used to identify potential compounds with greater biological activities and the compounds will be experimentally examined. 3) Investigate the mechanism of Bax activation on biological membranes by the Bax activators. We will use a novel patch-clamp technique combined with biochemical and cell biology approaches to investigate how the Bax activators induce Bax permeation channels on native biological membranes in vitro. We will also study how Bax permeation pore formation is regulated by the anti-apoptotic Bcl-2 protein Bcl-XL. As dysregulation of Bax expression has been implicated in lung tumor development, inducing apoptosis in tumor cells by directly activating Bax holds promise as a novel therapeutic strategy to treat lung cancer patients.